More and more high-power switching devices such as an IGBT (insulated gate bipolar transistor) module are used in power electronic equipment. Reliable operation of the IGBT is critical to proper functioning of power electronic systems. When the IGBT module shorts, the current flowing through the IGBT module is large, and thus the power loss of the IGBT module is large. Consequently, the IGBT module may likely be thermally broken down if no protection is quickly taken.
When the IGBT shorts occurs, the IGBT is turned off too quickly, a stray inductance exists on a busbar connected to the IGBT module, larger di/dt may generate a larger spike voltage, which may damage the IGBT module. In the application of high-power IGBT modules, soft turn off circuits or active clamping circuits are used. When the IGBTs need to be turned off in the event of overcurrent/short-circuit fault, the soft turn off circuits or the active clamping circuits can better suppress the spike voltage and can effectively protect the IGBT modules. For the occasion where a simple drive is used, due to particularities of the simple drive, the traditional soft turn off circuits or active clamping circuits are not applicable any more, and thus it is required to find new solutions.
Principles of “the simple drive” are as follows.
As shown in FIG. 1, a schematic block diagram of a traditional drive is illustrated. In FIG. 1, in the traditional drive, an energy pulse signal and a drive pulse signal are separately transmitted, Wherein the energy pulse signal contains power supply information, and the drive pulse signal contains drive information. That is, the energy pulse signal is transmitted from a control board to a drive board through an isolation transformer, and then is generated into a stable drive power supply by means of relevant circuits. Whereas the drive pulse signal is transmitted. from the control board to the drive board through another isolation transformer, and then is generated into a drive signal containing positive and negative voltages by means of the above generated drive power supply and a demodulation circuit to drive the IGBT to be turned on or turned off, wherein the drive power supply is used to supply power to the demodulation circuit.
As shown in FIG. 2, a schematic block diagram of a simple drive is illustrated. In FIG. 2, a control board outputs both an energy pulse signal and a drive pulse signal. After being transmitted through an isolation transformer, the energy pulse signal and the drive pulse signal charge/discharge a gate capacitor of the IGBT via a drive board to finally form a drive signal to drive the IGBT to be turned on or turned off Because circuits related to energy transmission are omitted, devices used in the simple drive are greatly reduced, such that the entire drive circuit is greatly simplified, power consumption is reduced, and reliability is improved.
In the simple drive circuit, the control board modulates a pulse width modulation (PWM) signal into a pulse signal Vwinding, which includes both an energy pulse signal and a drive pulse signal. The pulse signal is transmitted to the drive board through the isolation transformer, as shown in Vwinding in FIG. 3. The signal triggers a relevant switch tube in the control board to act and then charges/discharges the gate capacitor of the IGBT to finally form a gate voltage, as shown in VGE in FIG. 3. The VGE is formed by charging or discharging the gate capacitor by the pulse signal. Reference is made by taking an example where the VGE is positive. To reduce a magnetic core of the isolation transformer and ensure the magnetic core to be unsaturated, the pulse width of the pulse signal may be only a few microseconds, and the pulse signal can charge the gate capacitor to a VGE value (+15V) required to drive the IGBT. However, the pulse width of a real drive signal may be tens or hundreds of microseconds or even longer. If there is no refresh pulse signal, the gate capacitor may slowly discharge, causing the VGE to gradually decrease, such that a normal drive voltage cannot be reached. Therefore, the refresh pulse needs to charge the gate capacitor at intervals to maintain the gate voltage VGE. As for the time interval of the refresh pulse, it is mainly determined by a gate capacitor discharge time constant. In principle, the VGE does not drop too much before arrival of a next refresh pulse (for example, the VGE should not be lower than 14V before arrival of the next refresh pulse).
According to principles of the simple drive, the simple drive has no stable drive power supply. Therefore, traditional soft turn off circuits are no longer applicable. This is because there is no stable power supply to control the switch tube of the drive board, and thus it is impossible to switch a large resistor or a large capacitor after a fault signal is detected.
For the active clamping circuits, in some applications, a bus voltage may gradually rise. When the bus voltage exceeds a clamping value, transient voltage suppressors (TVS) may be broken down, and the active clamping circuits may continuously inject charges into the gate. Because there is no stable negative power supply, the gate voltage may likely be elevated above a threshold, which is prone to a fault of bridge arm direct connection.
Therefore, for application of the simple drive, a new drive circuit of a power semiconductor switch is needed.
The above-mentioned information disclosed in this Background section is only for the purpose of enhancing the understanding of background of the present disclosure and may therefore include information that does not constitute a prior art that is known to those of ordinary skill in the art.